The processing of semiconductor wafers and other integrated circuits (IC) includes critical manufacturing steps such as etching wafer surfaces and depositing layers of material on wafer surfaces to form device components, interconnecting lines, dielectrics, insulating barriers and the like. Various systems have been employed to deposit layers of material and the like on the surface of integrated circuits, and often such layers are formed by chemical vapor deposition (CVD). A conventional thermal CVD process deposits a stable chemical compound on the surface of a wafer by thermal reaction of certain gaseous chemicals. Various CVD reactors have been used in the art including low pressure CVD systems and atmospheric pressure CVD systems.
More recently, plasma enhanced (sometimes called plasma assisted) CVD systems (PECVD) have been developed. PECVD systems generally operate by disassociation and ionization of gaseous chemicals. The high electron temperatures associated with the plasma increase the density of the disassociated species available for deposition on the wafer surface. Accordingly, such systems are able to operate at lower temperatures than conventional thermal CVD systems. Such lower temperature processes are desirable and minimize diffusion of shallow junctions and inter diffusion of metals contained within the integrated circuits. Moreover, PECVD systems are suitable for forming multiple dielectric layers to be used to isolate stacked device features as device densities increase. When forming such multilayer dielectric layers it is desirable to provide a layer with good gap fill, isolation, stress and step coverage properties. These properties become more difficult to attain as device dimensions shrink.
In PECVD systems, the reactor is typically operated at low pressures during processing of the semiconductors. Such low pressures present particular gas flow dynamics considerations that must be addressed. With low pressures, the collision rate of the active species is relatively low and the mean-free path of the species is relatively long. Accordingly, it is desirable to provide a reactor capable of uniform, controlled gas flow within the process chamber, across the wafer, and to the exhaust, thus providing uniform processing of the wafer. Moreover, other operating pressures may be used for various processes, and thus it is desirable for the reactor to be capable of operating over a large pressure range.
Cleaning of the reactor plays an important role in the effective operation of a system. The highly reactive species deposit on the walls of the chamber, and the operating components, as well as on the surface of the substrate. Such deposits affect the operation of the system, may affect the plasma potentials within the system, and are a serious source of particulates which may end up contaminating the deposited film. Accordingly it is advantageous to provide a reactor design capable of self cleaning.